Distribution-free control chart


Distribution-free control charts are one of the most important tools of statistical process monitoring and control. Implementation techniques of distribution-free control charts do not require any knowledge about the underlying process distribution or its parameters. The main advantage of distribution-free control charts is its in-control robustness, in the sense that, irrespective of the nature of the underlying process distributions, the properties of these control charts remain same when the process is smoothly operating without presence of any assignable cause.
Early evidence of research on nonparametric control charts may be found in 1981 when P.K. Bhattacharya and D. Frierson introduced a nonparametric control chart for detecting small disorders. However, major growth of nonparametric control charting schemes has taken place only in the recent years.

Popular distribution-free control charts

There are distribution-free control charts for both Phase-I analysis and Phase-II monitoring.
One of the most notable distribution-free control chart for Phase-I analysis is RS/P chart proposed by G. Capizzi and G. Masaratto. RS/P chart separately monitor location and scale parameters of a univariate process using two separate charts. In 2019, Chenglong Li, Amitava Mukherjee and Qin Su proposed a single distribution-free control chart for Phase-I analysis using multisample Lepage statistic.
Some popular Phase-II distribution-free control charts for univariate continuous processes includes: